Koelling, Vanessa , Mauricio, Rodney .
Intrinsic barriers to hybridization are present between the rare cedar glade endemics Leavenworthia alabamica and L. crassa.
Post-mating reproductive barriers to gene flow between species play a role in speciation in many taxonomic groups. The mustard genus Leavenworthia is a historically important plant group in which numerous questions about speciation remain unanswered. Two sister species within the genus, L. alabamica and L. crassa, have been of particular interest to researchers since early work by Rollins and Lloyd on their taxonomy and mating system. These species exhibit extensive ecological overlap; yet can only be reliably distinguished based on fruit shape characters. What then prevents these species from hybridizing? In this study, we asked the question: are intrinsic reproductive barriers present at any stage of hybridization between L. alabamica and L. crassa?
To answer these questions, we performed crosses in the greenhouse between L. alabamica and L. crassa individuals from three populations of each species. Three individuals from different maternal lines in each population were randomly chosen, for a total of 18 plants used to generate F1 hybrids. Eighteen F1 hybrids were then crossed to generate F2 hybrids. We generated backcross hybrids using six F1 hybrid individuals and six F1 individuals derived from intraspecific crosses. The entirety of the experiment was performed twice. Seed set from each type of cross was analyzed using nested ANCOVA, with mean maternal plant ovule number as a covariate. Pollen viability was scored on each plant and analyzed using nested ANOVA. From these analyses, we conclude that although viable and fertile F1, F2, and backcross hybrids can be produced between these species, L. alabamica is more successful at receiving pollen from L. crassa than donating it, and vice versa. In addition, we found the phenomenon known as unilateral incompatibility in these species. Together, these two types of asymmetrical crossing barriers may have played a role in the speciation of L. alabamica and L. crassa.
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1 - University of Georgia, Genetics, Athens, GA, 30602, USA
asymmetrical crossing barrier
Presentation Type: Oral Paper:Papers for Topics
Location: Williford A/Hilton
Date: Tuesday, July 10th, 2007
Time: 11:30 AM